Nothing speeds up the demise of an A more than good ol quality time together ... and with your OW this is going to be like a pressure cooker.
At the moment you are the 'out' for W ... when W no longer has to 'sneak' around ... no fun, no rush .. and no reason to NOT be with OW, I can just feel the steel cage feeling close in on her. Her circus and her monkeys ... and yeah you are right .. when she does escape for her 'break' its Slumdog time and reality of "WTF have I done" sets in.
I have this image of a war scene from BraveHeart in my head ... the enemy forces are rapidly approaching on horse back, the ground troops await the stampeded ... little does anyone know they have long spears hidden but must wait till the last second and BraveHeart continues to shout the order "Hold"
Stay the course Dif, she needs this ... and better yet I feel you do to, listen to my advice and use this time to build yourself .... its golden.